This invention relates to curable polyorganosiloxane (silicone) compositions particularly adapted for use in electronic potting applications.
Because of their excellent thermal stability, low temperature flexibility and high dielectric strength, silicones have been used for potting and encapsulating electrical devices such as integrated circuits. They are typically used as elastomeric or gel-like materials providing shock, vibrational and thermal stress protection on fragile electronic components. References relating generally to silicone gel encapsulants include U.S. Pat. Nos. 3,933,712; 4,072,635; 4,087,585; 4,271,425; 4,374,967; and D. Dickson, Jr., Proceedings Electric/Electronic Intel. Conf. 12, 92(1975). See also prior art description in U.S. Pat. No. 4,374,967. The present commercially available potting silicones include one component compositions such as U.S. Pat. No. 4,271,425 which are cured by moisture, requiring from several hours to days to complete the cure. Faster cures may be obtained from two component systems such as those in U.S. Pat. No. 4,087,585 if elevated temperatures are provided. The two-component systems which require a platinum catalyst, however, are inhibited by organotin compounds, sulfur, amines, urethanes and unsaturated hydrocarbon plasticizers on the substrate surfaces.
It is known that certain silicones containing methacrylate or acrylate functional groups may be cured by ultraviolet light. U.S. Pat. Nos. 4,201,808 and 4,348,454 and U.K. Patent Application No. GB 2039287A all describe UV curing compositions of silicones containing methacrylates or acrylates for paper release coatings. The compositions do not produce jelly-like or elastomeric materials.
Accordingly, it is desirable to have a UV curable silicone composition which will produce an elastomeric or soft gel consistency upon curing. Furthermore, it is desirable that the composition be capable of curing by another mechanism in areas which are not readily accessible by UV irradiation.